The iPrint&Scan (iTunes link) app will print the photos from your photo albums, print straight from the phone's camera, or scan documents into the printer to pipe them on to your phone.
You don't need a computer or a driver, but you do need to be on the same network as a suitable Brother printer. There are a handful of settings -- a couple of paper size options, glossy or plain paper, and black and white or colour scanning. And you can only print a maximum of five copies.
It's a limited app, but if you already have a Brother printer -- or you're thinking of buying a new printer -- the app is free and it could sway your choice.
What's a brother to do if he has an Android phone? Just be patient, because Brother is working on an app for the little green robot too.